In many applications it is desired to arrange a plurality of printed circuit boards in a parallel array, and to provide a means for interconnecting the conductive traces of each board with associated traces of the adjacent boards by means of electrical connectors, in a manner permitting the boards to be separated and replaced if desired. For convenience it is desired that the interconnected traces be disposed aligned with each other, and the electrical connectors for interconnecting the associated traces thus can be arranged in one stack perpendicular to the boards. Such connectors have arrays of contacts extending perpendicularly with respect to the boards and have post sections extending through plated through-holes of a board for electrical connection to the board's traces while having male contact sections on one side of the board and female contact sections on the other side; thus the contacts of each connector are adapted to mate with corresponding contacts of a matable connector by means of cooperating male and female contact sections. One of the connector housings is a plug which is matably received into the other housing which is a shroud, and the connectors are thus said to be stackable.
One type of stackable connector is sold by AMP Incorporated, Harrisburg, Pa. under Part No. 533650. Also two types of electrical contacts are sold by AMP Incorporated having box-like female contacts matable with square post male contact sections, under Part No. 533667 having a compliant spring section for self-retaining within a plated through-hole of a board, and under Part No. 1-532466-5 having square post sections for wire wrapping by conductor wires.
Traces of many printed circuit boards are generally manufactured to have a width of 0.015 inches, for a certain plated metal thickness to provide certain nominal current-carrying characteristics. Traces must be spaced from each other a minimum distance of 0.005 inches to minimize inductance effects and noise; a trace spacing of 0.010 to 0.012 inches is commonly used to facilitate accuracy during trace plating procedures. Commonly the plated through-holes to which traces extend are arrayed in a closely spaced arrangement for convenience and have a generally accepted nominal hole diameter of 0.038 inches, with the centerlines of the holes being spaced 0.100 inches apart. With a ring of plating material having a width of at least 0.002 inches required peripherally around each plated through-hole, the plated through-holes generally have a maximum spacing between nearest through-hole plating material peripheral edges of at most about 0.058 inches, and the spacing is even less where peripheral conductive pads of 0.015 inches width are used surrounding unplated through-holes for soldering to contacts. In such boards it is required that the traces be spaced a finite small distance from any plating material through or around each hole to avoid short circuiting or bridging especially resulting from eventual soldering operations. In cetain such arrays it is necessary for traces extending to certain holes to pass between holes for others of the traces and be spaced at least the minimum spacing from plating material edges around the holes. Where two traces must pass between adjacent through-holes a minimum distance must be maintained between the two traces and also between each trace and the plating material surrounding each through-hole.
Connectors for such boards have contacts adapted to provide an assured electrical connection to the plating material of the through-holes, and one common type of contact has a square cross-section within the 0.038 inch diameter hole, with dimensions of 0.025 inches by 0.025 inches, establishing a diagonal between opposed corners of about 0.037 inches. The male or post contact section at one end of the contact has continuously therealong the same square cross-section of 0.025 by 0.025 inches, and the female contact section at the other end has a receptacle structure correspondingly adapted to receive a square post of the same dimensions and establish an assured electrical connection therewith by central portions of four elongate arcuate spring arms about 0.016 inches wide engageable with central portions of the flat surfaces along the four sides of the square post. The spring contact arms of the known receptacle contact section are adapted to establish appropriate levels of contact normal force biased against the flat post sides for assured electrical connection, given the 0.025 dimension between the side surfaces of the post.
It is desired among manufacturers of printed circuit boards to reduce the real estate taken up by the through-hole array needed for board interconnection, or to increase the number of through-holes in a given area. Where the holes of conventional diameter of 0.038 inches are moved to have a closer spacing of 0.075 inches, the spacing between conductive material of adjacent through-holes is reduced to 0.033 inches. Where it is desired that the traces continue to maintain their width of 0.015 inches and existing thickness and resultant current-carrying characteristics, the spacing between two traces between adjacent holes and between each trace and the nearby hole becomes unacceptably small, commonly leading to unacceptable inductance effects and noise or else susceptibility to bridging from soldering. Where the 0.038 inch diameter holes are unplated and have 0.015 inch wide conductive peripheral pads or rings therearound for soldering, the distance from an edge of even a single trace to the nearby conductive pad may also become unacceptably small.
It is desired that the contacts of the connectors for interconnecting the boards maintain their square shape and their 0.025 by 0.025 side to side dimensions and meet existing electrical current-carrying requirements, and also mate with the known receptacle contact section having proven reliable mating properties, and to some extent maintain structural strength. Therefore the hole diameter of the board through-holes would seemingly have to be maintained at 0.038 inches to accommodate the post diagonal of about 0.037 inches of such contacts, and rerouting of traces would have to be adopted so that no two traces would have to extend between any adjacent through-holes.
Yet it remains desired to provide a system of interconnecting connectors for 0.075 centerline spacing which permits a pair of traces to extend between adjacent plated through-holes at that spacing, or which permits a single trace to extend between solder pads of adjacent unplated through-holes.